1. Field of the Invention
The present invention pertains to rotary printing presses and, more particularly, to the control of the temperature of the plate on a cylinder in such presses.
2. Description of the Related Art
The temperature of the plate on a cylinder of a rotary printing press is important in maintaining printing quality as the ability to achieve proper inking of the plate is related to temperature. If the plate temperature is too high, the ink viscosity drops. Thus, the ink breaks down and tends to adhere to the nonimage bearing areas of the plate. Improper inking may also occur when the plate temperature is too low.
U.S. Pat. No. 2,971,460 issued to Shindle in 1961 and discloses a system for controlling ink roller temperature in a printing press by means of water circulating through the hollow interior of the rollers. This system is primarily concerned with heating of the rollers with heat extracted from web cooling rollers. When cooling of the inking rollers is necessary, the system relies on the use of cold water from an external source with the subsequent discharge of the water to a drain. However, such an open circulation system is wasteful of water.
Temperature control in the Shindle system is by way of thermostatic valves which are responsive to the water temperature which is, effectively, only an indirect measurement of the inking roller temperature.
Modern rotary presses and the inks used therewith are such that cooling, rather than heating, of the inking train and printing plate has primary importance. It is, accordingly, a primary object of the present invention to provide a system for effecting such cooling in an efficient, water-conserving manner.
In the printing process, the critical temperature for proper inking is that of the printing plate itself. It is also a principal object of the present invention to provide a temperature control system which is directly responsive to the plate temperature.
A further object of the invention is the provision of such a temperature control system which is capable of either cooling or heating the printing plate.